RCD & Test and Tag Functional, correctly wired RCDs "should" prevent an unlucky soul from becoming the dearly departed in most circumstances Rob, however there are at least four possible scenarios where even if the RCD trips at its rated leakage current within the time limit, they will receive a zap that proves lethal.
The Electrical (Safety) Regs don't "require" items to be tested & tagged, but a current tag indicating an item has been inspected and tested IAW AS/NZS3760 is a method to get to "deemed safe", a history of test results provides evidence of an items safety over the period of time an item has been the subject of regular testing.
There are some obvious limitations of TnT, it depends on the skill, training, knowledge, equipment and enthusiasm of the person performing the inspection and tests. It is a snapshot of how something is at the time it was tested, I've TnT'ed a tool in a builders shed one afternoon, gone back to finish off the following morning and found that tool back in the rack with a damaged lead and my tag removed.
I would suggest that your installation RCDs are tested annually and their correct operation confirmed, depending on the nature of your work and the use tools and other electrical equipment are put to, and the environment these items are used in, possibly look at longer retest intervals. This assessment should ideally be documented for future reference.